This invention relates to a novel oxypropylene polymer which contains a reactive silicon group and to a method of producing the same.
So far, various room temperature curing polymers have been developed which can be cured to rubber-like substances by the action of moisture. Thus, oxypropylene polymers containing a reactive silicon group (a group which is a silicon atom-containing group with a hydroxyl group or a hydrolyzable group being bound to the silicon atom and can form a siloxane bond) are also known.
However, since it is difficult to produce high molecular weight polyoxypropylene with a narrow molecular weight distribution (great monodispersity), the known reactive silicon group-containing polyoxypropylene species are only those showing a broad molecular weight distribution (great polydispersity).
Recently, it has been reported that polyoxypropylene with a narrow molecular weight distribution can be obtained. The present inventors found that polymers derived from polyoxypropylene having a narrow molecular weight distribution, which is used as the main chain, by introducing a reactive silicon group and a urethane bond terminally to the main chain, have a low viscosity, hence are easy to handle, before curing and, after curing, give cured products having excellent tensile characteristics as well as good chemical resistance and water resistance. This finding has now led to the present invention.
The reactive silicon group-containing oxypropylene polymer of this invention is an oxypropylene polymer the main polymer chain of which is essentially composed of a repeating unit of the formula 
and which has at least one terminal reactive silicon group and at least one terminal urethane bond. It has an {overscore (M)}w/{overscore (M)}n ratio of not more than 1.5 and a number average molecular weight of not less than 3,000.
The production method of this invention is characterized by reacting an oxypropylene polymer having an {overscore (M)}w/{overscore (M)}n ratio of not more than 1.5 and a number average molecular weight per terminal functional group of not less than 1,500 with a compound having a reactive silicon group and an isocyanato group.
The xe2x80x9creactive silicon groupxe2x80x9d as so termed herein is not limited to any particular species but may typically include groups of the general formula (1) shown below: 
In the above formula, R1 and R2 each is an alkyl group containing 1 to 20 carbon atoms, an aryl group containing 6 to 20 carbon atoms, an aralkyl group containing 7 to 20 carbon atoms or a triorganosiloxy group of the formula (Rxe2x80x2)3SiOxe2x80x94. Where there are two or more R1 or R2 groups, they may be the same or different. Rxe2x80x2 is a monovalent hydrocarbon group containing 1 to 20 carbon atoms. The three Rxe2x80x2 groups may be the same or different. X is a hydroxyl group or a hydrolyzable group and, where there are two or more X groups, they may be the same or different. a is 0, 1, 2 or 3 and b is 0, 1 or 2. The number b may vary in the m groups of the formula 
m is an integer of 0 or 1 to 19. The following condition shall be satisfied: a+xcexa3bxe2x89xa71.
The hydrolyzable group represented by the above-mentioned X is not particularly limited but may be any hydrolyzable group known in the art. More specifically, there may be mentioned a hydrogen atom, a halogen atom, an alkoxy group, an acyloxy group, a ketoximato group, an amino group, an amido group, an acid amido group, an aminoxy group, a mercapto group, an alkenyloxy group and the like. Among these, the hydrogen atom and alkoxy, acyloxy, ketoximato, amino, amido, aminoxy, mercapto and alkenyloxy groups are preferred. From the viewpoint of mild hydrolyzability and easy handling, alkoxy groups are particularly preferred.
One to three such hydrolyzable groups or hydroxyl groups may be bound to one silicon atom, and (a+xcexa3b) is preferably equal to 1 to 5. Where there are two or more hydrolyzable groups or hydroxyl groups in the reactive silicon group, they may be the same or different.
The reactive silicon group may contain one silicon atom or two or more silicon atoms. In the case of a reactive silicon group comprising silicon atoms linked to one another via a siloxane bonding or the like, the group may contain about 20 silicon atoms.
Reactive silicon groups of the following general formula (2) are preferred because of ready availability. 
In the above formula, R2, X and a are as defined above.
Specific examples of R1 and R2 appearing in the general formula (1) given hereinabove include, among others, alkyl groups, such as methyl and ethyl, cycloalkyl groups, such as cyclohexyl, aryl groups, such as phenyl, aralkyl groups, such as benzyl, and triorganosiloxy groups of the formula (Rxe2x80x2)3SiOxe2x80x94 in which Rxe2x80x2 is methyl or phenyl. Among these, methyl is particularly preferred.
The oxypropylene polymer should recommendably contain at least one, preferably 1.1 to 5 reactive silicon groups per molecule thereof. When the number of reactive silicon groups contained in the polymer on a per-molecule basis is less than 1, the curability becomes inadequate and good rubber elastic behavior can hardly be developed.
The oxypropylene polymer contains at least one reactive silicon group terminally to the molecular chain thereof. It may contain a reactive silicon group internally to the chain. When the reactive silicon group occurs terminally to the molecular chain, as in the present invention, the oxypropylene polymer component contained in the finally-formed cured products can have an increased number of effective network chains and therefore a rubber-like cured product showing high strength and high elongation (low elasticity) can readily be obtained.
The xe2x80x9curethane bondxe2x80x9d so termed herein means a bond represented by xe2x80x94NHCOOxe2x80x94.
The oxypropylene polymer, which constitutes the main polymer chain in the polymer of this invention, is essentially composed of a repeating unit of the formula 
This oxypropylene polymer may be straight-chained or branched, or a mixture of these. It may further contain a small proportion of another monomer unit or the like.
The oxypropylene polymer that can effectively be used has a number average molecular weight of not less than 3,000. The number average molecular weight of the polymer should preferably be not less than 3,000 when the polymer is straight-chained, and not less than 5,000 when the polymer is branched. More preferably, the polymer should have a number average molecular weight of 6,000 to 30,000. Furthermore, in this oxypropylene polymer, the weight average molecular weight/number average molecular weight ratio ({overscore (M)}w/{overscore (M)}n) is not more than 1.5, hence the molecular weight distribution is very narrow (the monodispersity is great). The value of {overscore (M)}w/{overscore (M)}n should preferably be not more than 1.4, more preferably not more than 1.3. The molecular weight distribution can be measured by various methods. Generally, however, the measurement method most commonly used is gel permeation chromatography (GPC). Since the molecular weight distribution is narrow in that manner despite the great number average molecular weight, the polymer of the invention has a low viscosity before curing, hence is easy to handle and, after curing, shows good rubber elastic behavior.
The polymer of this invention has a terminal urethane bond, so that the cured products after curing are excellent in strength and elongation.
For producing the reactive silicon group-containing oxypropylene polymer of the invention, it is only necessary to react an oxypropylene polymer having a terminal functional group (hereinafter referred to as functional group Y), such as a hydroxyl group, with a compound having a reactive silicon group and an isocyanato group reactive with functional group Y.
The functional group Y-containing oxypropylene polymer to be used should be an oxypropylene polymer having an {overscore (M)}w/{overscore (M)}n ratio of not more than 1.5 and a number average molecular weight per terminal functional group of not less than 1,500.
The isocyanato group- and reactive silicon group-containing compound includes, but is not limited to, such typical examples as xcex3-isocyanatopropyltriethoxysilane, xcex3-isocyanatopropylmethyldimethoxysilane, xcex3-isocyanatopropyltrimethoxysilane and the like isocyanato-containing silanes.
The production method of the invention which comprises reacting an oxypropylene polymer having a terminal functional group Y with a compound having an isocyanato group and a reactive silicon group, as mentioned above, allows introduction of the reactive silicon group in one step without necessitating complicated prior art reaction steps.
The reactive silicon group-containing oxypropylene polymer of the invention, when exposed to air, forms a three-dimensional network under the action of moisture and hardens to a solid having rubber-like elasticity.
In curing the polymer of this invention, a silanol condensing catalyst (curing catalyst) may be used or may not be used. When a silanol condensing catalyst is used, it may be selected from a wide variety of known ones. As typical examples thereof, there may be mentioned such silanol condensing catalysts as titanate esters, such as tetrabutyl titanate and tetrapropyl titanate; tin carboxylate salts, such as dibutyltin dilaurate, dibutyltin maleate, dibutyltin diacetate, tin octanoate and tin naphthenate; reaction products from dibutyltin oxide and phthalate esters; dibutyltin diacetylacetonate; organic aluminum compounds, such as aluminum trisacetyl-acetonate, aluminum tris ethyl acetoacetate) and diisopropoxyaluminum ethyl acetoacetate; chelate compounds such as zirconium tetracetylacetonate and titanium tetracetylacetonate; lead octanoate; amine compounds, such as butylamine, octylamine, dibutylamine, monoethanolamine, diethanolamine, triethanolamine, diethylenetriamine, triethylenetetramine, oleylamine, cyclohexylamine, benzylamine, diethylaminopropylamine, xylylenediamine, triethylenediamine, guanidine, diphenylguanidine, 2,4,6-tris(dimethylaminomethyl)phenol, morpholine, N-methylmorpholine, 2-ethyl-4-methylimidazole and 1,8-diazabicyclo-[15.4.0]undecene-7 (DBU), salts of such amine compounds with carboxylic acids and so forth; low molecular weight polyamide resins obtained from an excess of a polyamine and a polybasic acid; reaction products from an excess of a polyamine and an epoxy compound; amino-containing silane coupling agents, such as xcex3-aminopropyltrimethoxysilane and N-(xcex2-aminoethyl)-aminopropylmethyldimethoxysilane; and other known silanol condensing catalysts, such as acid catalysts and basic catalysts. These catalysts may be used either singly or in combination in the form of a mixture of two or more of them.
These silanol condensing catalysts are used preferably in an amount of about 0.1 to 20 parts by weight, more preferably about 1 to 10 parts by weight, per 100 parts by weight of the oxypropylene polymer. When the amount of the silanol condensing catalyst is too small as compared with the oxypropylene polymer, the rate of curing may be slow in certain instances and the curing reaction can hardly proceed to a satisfactory extent in some instances. On the other hand, if the amount of the silanol condensing catalyst is too large relative to the oxypropylene polymer, local heat generation and/or foaming may occur during curing, unfavorably making it difficult to obtain good cured products.
The reactive silicon group-containing oxypropylene polymer of the invention may be modified by incorporating thereinto various fillers. Usable as the fillers are reinforcing fillers such as fumed silica, precipitated silica, silicic anhydride, hydrous silicic acid and carbon black; fillers such as calcium carbonate, magnesium carbonate, diatomaceous earth, calcined clay, clay, talc, titanium oxide, bentonite, organic bentonite, ferric oxide, zinc oxide, active zinc white, and xe2x80x9cshirasuxe2x80x9d balloons; and fibrous fillers such as asbestos, glass fibers and filaments.
For obtaining cured compositions affording high strength using such fillers, a filler selected from among fumed silica, precipitated silica, anhydrous silicic acid, hydrous silicic acid, carbon black, surface-treated finely divided calcium carbonate, calcined clay, clay, active zinc white and the like is used in the main in an amount within the range of 1 to 100 parts by weight per 100 parts by weight of the reactive silicon group-containing oxypropylene polymer to give favorable results. For obtaining cured compositions affording low strength and high elongation, a filler selected from among titanium oxide, calcium carbonate, magnesium carbonate, talc, ferric oxide, zinc oxide, xe2x80x9cshirasuxe2x80x9d balloons and the like is used in the main in an amount within the range of 5 to 200 parts by weight per 100 parts by weight of the reactive silicon group-containing oxypropylene polymer to give favorable results. Of course, these fillers may be used either alone or in combination as a mixture of two or more of them.
In using the reactive silicon group-containing oxypropylene polymer in accordance with the invention, a plasticizer may be used more effectively in combination with the filler since the use thereof may provide the cured products with an increased elongation and/or allow incorporation of fillers in large amounts. This plasticizer is any one in common and general use. Thus, for instance, phthalate esters, such as dioctyl phthalate, dibutyl phthalate and butyl benzyl phathalate; aliphatic dibasic acid esters, such as dioctyl adipate, isodecyl succinate and dibutyl sebacate; glycol esters, such as diethylene glycol dibenzoate and pentaerythritol esters; aliphatic esters, such as butyl oleate and methyl acetylricinoleate; phosphate esters, such as tricresyl phosphate, trioctyl phosphate and octyl diphenyl phosphate; epoxy plasticizers, such as epoxidized soybean oil, and benzyl epoxystearate; polyester plasticizers, such as polyesters from a dibasic acid and a dihydric alcohol; polyethers, such as polypropylene glycol and derivatives thereof; polystyrenes, such as poly-xcex1-methylstyrene and polystyrene; polybutadiene, butadiene-acrylonitrile copolymer, polychloroprene, polyisoprene, polybutene, chlorinated paraffin, and so forth may be used either singly or in combination in the form of a mixture of two or more of them, as desired. Favorable results are obtained when the plasticizer is used in an amount within the range of 0 to 100 parts by weight per 100 parts by weight of the reactive silicon group-containing oxypropylene polymer.
In using the reactive silicon group-containing oxypropylene polymer of the invention, various additives, such as tackifiers (e.g. phenol resins, epoxy resins), adhesion improvers, physical property modifiers, storage stability improvers, antioxidants, ultraviolet absorbers, metal inactivators, antiozonants, light stabilizers, amine-type radical chain inhibitors, phosphorus-containing peroxide decomposing agents, lubricants, pigments, blowing agents, etc., may be added to the polymer as necessary each in an appropriate amount to give room temperature curable compositions.